Louis van Gaal's defensive options at Manchester United are dwindling by the dayGetty

What's worse than having two of your first-choice options at centre-half unavailable? How about three of them? Or maybe four? That inexplicable situation looks to have befallen Manchester United manager Louis van Gaal, who has seen his already meagre defensive options decimated by injury.

Jonny Evans looks set to join Phil Jones on the sidelines after injuring his ankle in the 5-3 defeat to Leciester City. Van Gaal lost another option in that game when Tyler Blackett, who had been ever-present in the Dutchman's starting XI this season, was shown a straight red card.

News that Chris Smalling has now suffered a leg injury confirms the malaise at United has reached unfathomable levels.

Questions will again be asked of the club's summer transfer policy but revisionism will do little to aid Van Gaal, with the visit of West Ham United looming on Saturday 27 September and Everton a week later.

When Sam Allardyce's side come to town, United will have the sole option of Marcos Rojo at centre-half, the club's £16m signing who spent the summer and the early stages of his United career playing at left-back.

The Argentine's inclusion is assured by virtue of there simply being no one else but who will partner him?

Jonny Evans set to join United's injured listGetty

United's Under-21 captain, Tom Thorpe, seems a logical solution. The 21-year-old has yet to feature for the first team at any capacity during Van Gaal's reign, having been left out of club's pre-season tour of the US. His commanding performances at centre-half over the years have raised questions why.

While the likes of Paul Pogba, Ravel Morrison, Ryan Tunnicliffe, Will Keane and Jesse Lingard have all progressed for better or for worse, Thorpe is one of the last men remaining from United's 2011 Youth Cup success.

His leadership qualities suggest he is of the right character to grasp the challenge Van Gaal has relentlessly promised to hand to young players, while his outings in midfield over the years suggest he is comfortable enough with the ball to seamlessly absorb the Dutchman's directive.

But Thorpe's continued omission has raised concerns over his future, none more so prevalent than the incident when he failed to make the starting XI in the largely experimental side that lost 4-0 to MK Dons in the League Cup, where full-back Marnick Vermijl was handed one of the three central defence roles ahead of the Under-21 skipper.

You feel if Thorpe is not handed his chance on Saturday against the Hammers, his future lies away from Manchester.

Paddy McNair is another name to be suggested in the wake of the injury epidemic consuming United's backline. However, the 19-year-old's selection ahead of Thorpe would sadly be considered another damning indictment of Thorpe's chances at the club.

Northern Irish youngster McNair has featured alongside his older teammate in defence for the Under-21s this season, having made the step up from the Under-18s the previous term.

Argentine defender Marcos Rojo will be likely to play at centre-halfGetty

Previously a diminutive midfielder – with United academy coach Paul McGuinness once likening him to Michael Carrick – McNair's early appearances in defence were a direct result of injuries within the Under-18 ranks.

While he has continued at the heart of defence this season in Warren Joyce's side, the Under-21 boss has suggested the teenager could once again move further up the pitch this season. Is that a trait van Gaal wants in his backline?

Realistic options within the club's Under-21 ranks stop short at those two. With Michael Keane on loan at Burnley until January, Van Gaal has little choice but to consider alternatives within his current squad.

The penchant of utilising Michael Carrick at centre-half seems to have been passed down from manager to manager in recent years but the former Netherlands boss will not have that option until the 33-year-old recovers from an ankle injury.

Daley Blind was used as a left-sided centre-half by Van Gaal during the World Cup semi-final against Argentina. Could the Dutchman reinstate the 3-5-2 formation to accommodate the 24-year-old in a back three?

It seems very unlikely, given the lack of a third body capable of filling the third centre-half role next to Rojo. And with United's attacking contingent beginning to click, destabilising that with a tactical reshuffle could create more problems than solutions.

The spate of injuries will leave many United fans in the unusual position of counting the days until the next international break and some respite from the league schedule. Eleven days and two Premier League fixtures come before that. Van Gaal, and what remains of his dilapidated defence, must find a way of navigating through that without any more setbacks.